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  <div class="section" id="numpy-ma-masked-where">
<h1>numpy.ma.masked_where<a class="headerlink" href="#numpy-ma-masked-where" title="Permalink to this headline">¶</a></h1>
<dl class="function">
<dt id="numpy.ma.masked_where">
<code class="sig-prename descclassname">numpy.ma.</code><code class="sig-name descname">masked_where</code><span class="sig-paren">(</span><em class="sig-param">condition</em>, <em class="sig-param">a</em>, <em class="sig-param">copy=True</em><span class="sig-paren">)</span><a class="reference external" href="https://github.com/numpy/numpy/blob/v1.18.1/numpy/ma/core.py#L1836-L1951"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#numpy.ma.masked_where" title="Permalink to this definition">¶</a></dt>
<dd><p>Mask an array where a condition is met.</p>
<p>Return <em class="xref py py-obj">a</em> as an array masked where <em class="xref py py-obj">condition</em> is True.
Any masked values of <em class="xref py py-obj">a</em> or <em class="xref py py-obj">condition</em> are also masked in the output.</p>
<dl class="field-list simple">
<dt class="field-odd">Parameters</dt>
<dd class="field-odd"><dl class="simple">
<dt><strong>condition</strong><span class="classifier">array_like</span></dt><dd><p>Masking condition.  When <em class="xref py py-obj">condition</em> tests floating point values for
equality, consider using <code class="docutils literal notranslate"><span class="pre">masked_values</span></code> instead.</p>
</dd>
<dt><strong>a</strong><span class="classifier">array_like</span></dt><dd><p>Array to mask.</p>
</dd>
<dt><strong>copy</strong><span class="classifier">bool</span></dt><dd><p>If True (default) make a copy of <em class="xref py py-obj">a</em> in the result.  If False modify
<em class="xref py py-obj">a</em> in place and return a view.</p>
</dd>
</dl>
</dd>
<dt class="field-even">Returns</dt>
<dd class="field-even"><dl class="simple">
<dt><strong>result</strong><span class="classifier">MaskedArray</span></dt><dd><p>The result of masking <em class="xref py py-obj">a</em> where <em class="xref py py-obj">condition</em> is True.</p>
</dd>
</dl>
</dd>
</dl>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<dl class="simple">
<dt><a class="reference internal" href="numpy.ma.masked_values.html#numpy.ma.masked_values" title="numpy.ma.masked_values"><code class="xref py py-obj docutils literal notranslate"><span class="pre">masked_values</span></code></a></dt><dd><p>Mask using floating point equality.</p>
</dd>
<dt><a class="reference internal" href="numpy.ma.masked_equal.html#numpy.ma.masked_equal" title="numpy.ma.masked_equal"><code class="xref py py-obj docutils literal notranslate"><span class="pre">masked_equal</span></code></a></dt><dd><p>Mask where equal to a given value.</p>
</dd>
<dt><a class="reference internal" href="numpy.ma.masked_not_equal.html#numpy.ma.masked_not_equal" title="numpy.ma.masked_not_equal"><code class="xref py py-obj docutils literal notranslate"><span class="pre">masked_not_equal</span></code></a></dt><dd><p>Mask where <em class="xref py py-obj">not</em> equal to a given value.</p>
</dd>
<dt><a class="reference internal" href="numpy.ma.masked_less_equal.html#numpy.ma.masked_less_equal" title="numpy.ma.masked_less_equal"><code class="xref py py-obj docutils literal notranslate"><span class="pre">masked_less_equal</span></code></a></dt><dd><p>Mask where less than or equal to a given value.</p>
</dd>
<dt><a class="reference internal" href="numpy.ma.masked_greater_equal.html#numpy.ma.masked_greater_equal" title="numpy.ma.masked_greater_equal"><code class="xref py py-obj docutils literal notranslate"><span class="pre">masked_greater_equal</span></code></a></dt><dd><p>Mask where greater than or equal to a given value.</p>
</dd>
<dt><a class="reference internal" href="numpy.ma.masked_less.html#numpy.ma.masked_less" title="numpy.ma.masked_less"><code class="xref py py-obj docutils literal notranslate"><span class="pre">masked_less</span></code></a></dt><dd><p>Mask where less than a given value.</p>
</dd>
<dt><a class="reference internal" href="numpy.ma.masked_greater.html#numpy.ma.masked_greater" title="numpy.ma.masked_greater"><code class="xref py py-obj docutils literal notranslate"><span class="pre">masked_greater</span></code></a></dt><dd><p>Mask where greater than a given value.</p>
</dd>
<dt><a class="reference internal" href="numpy.ma.masked_inside.html#numpy.ma.masked_inside" title="numpy.ma.masked_inside"><code class="xref py py-obj docutils literal notranslate"><span class="pre">masked_inside</span></code></a></dt><dd><p>Mask inside a given interval.</p>
</dd>
<dt><a class="reference internal" href="numpy.ma.masked_outside.html#numpy.ma.masked_outside" title="numpy.ma.masked_outside"><code class="xref py py-obj docutils literal notranslate"><span class="pre">masked_outside</span></code></a></dt><dd><p>Mask outside a given interval.</p>
</dd>
<dt><a class="reference internal" href="numpy.ma.masked_invalid.html#numpy.ma.masked_invalid" title="numpy.ma.masked_invalid"><code class="xref py py-obj docutils literal notranslate"><span class="pre">masked_invalid</span></code></a></dt><dd><p>Mask invalid values (NaNs or infs).</p>
</dd>
</dl>
</div>
<p class="rubric">Examples</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">import</span> <span class="nn">numpy.ma</span> <span class="k">as</span> <span class="nn">ma</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">a</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">arange</span><span class="p">(</span><span class="mi">4</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">a</span>
<span class="go">array([0, 1, 2, 3])</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">ma</span><span class="o">.</span><span class="n">masked_where</span><span class="p">(</span><span class="n">a</span> <span class="o">&lt;=</span> <span class="mi">2</span><span class="p">,</span> <span class="n">a</span><span class="p">)</span>
<span class="go">masked_array(data=[--, --, --, 3],</span>
<span class="go">             mask=[ True,  True,  True, False],</span>
<span class="go">       fill_value=999999)</span>
</pre></div>
</div>
<p>Mask array <em class="xref py py-obj">b</em> conditional on <em class="xref py py-obj">a</em>.</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">b</span> <span class="o">=</span> <span class="p">[</span><span class="s1">&#39;a&#39;</span><span class="p">,</span> <span class="s1">&#39;b&#39;</span><span class="p">,</span> <span class="s1">&#39;c&#39;</span><span class="p">,</span> <span class="s1">&#39;d&#39;</span><span class="p">]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">ma</span><span class="o">.</span><span class="n">masked_where</span><span class="p">(</span><span class="n">a</span> <span class="o">==</span> <span class="mi">2</span><span class="p">,</span> <span class="n">b</span><span class="p">)</span>
<span class="go">masked_array(data=[&#39;a&#39;, &#39;b&#39;, --, &#39;d&#39;],</span>
<span class="go">             mask=[False, False,  True, False],</span>
<span class="go">       fill_value=&#39;N/A&#39;,</span>
<span class="go">            dtype=&#39;&lt;U1&#39;)</span>
</pre></div>
</div>
<p>Effect of the <a class="reference internal" href="numpy.ma.copy.html#numpy.ma.copy" title="numpy.ma.copy"><code class="xref py py-obj docutils literal notranslate"><span class="pre">copy</span></code></a> argument.</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">c</span> <span class="o">=</span> <span class="n">ma</span><span class="o">.</span><span class="n">masked_where</span><span class="p">(</span><span class="n">a</span> <span class="o">&lt;=</span> <span class="mi">2</span><span class="p">,</span> <span class="n">a</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">c</span>
<span class="go">masked_array(data=[--, --, --, 3],</span>
<span class="go">             mask=[ True,  True,  True, False],</span>
<span class="go">       fill_value=999999)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">c</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="o">=</span> <span class="mi">99</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">c</span>
<span class="go">masked_array(data=[99, --, --, 3],</span>
<span class="go">             mask=[False,  True,  True, False],</span>
<span class="go">       fill_value=999999)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">a</span>
<span class="go">array([0, 1, 2, 3])</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">c</span> <span class="o">=</span> <span class="n">ma</span><span class="o">.</span><span class="n">masked_where</span><span class="p">(</span><span class="n">a</span> <span class="o">&lt;=</span> <span class="mi">2</span><span class="p">,</span> <span class="n">a</span><span class="p">,</span> <span class="n">copy</span><span class="o">=</span><span class="kc">False</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">c</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="o">=</span> <span class="mi">99</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">c</span>
<span class="go">masked_array(data=[99, --, --, 3],</span>
<span class="go">             mask=[False,  True,  True, False],</span>
<span class="go">       fill_value=999999)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">a</span>
<span class="go">array([99,  1,  2,  3])</span>
</pre></div>
</div>
<p>When <em class="xref py py-obj">condition</em> or <em class="xref py py-obj">a</em> contain masked values.</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">a</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">arange</span><span class="p">(</span><span class="mi">4</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">a</span> <span class="o">=</span> <span class="n">ma</span><span class="o">.</span><span class="n">masked_where</span><span class="p">(</span><span class="n">a</span> <span class="o">==</span> <span class="mi">2</span><span class="p">,</span> <span class="n">a</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">a</span>
<span class="go">masked_array(data=[0, 1, --, 3],</span>
<span class="go">             mask=[False, False,  True, False],</span>
<span class="go">       fill_value=999999)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">b</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">arange</span><span class="p">(</span><span class="mi">4</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">b</span> <span class="o">=</span> <span class="n">ma</span><span class="o">.</span><span class="n">masked_where</span><span class="p">(</span><span class="n">b</span> <span class="o">==</span> <span class="mi">0</span><span class="p">,</span> <span class="n">b</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">b</span>
<span class="go">masked_array(data=[--, 1, 2, 3],</span>
<span class="go">             mask=[ True, False, False, False],</span>
<span class="go">       fill_value=999999)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">ma</span><span class="o">.</span><span class="n">masked_where</span><span class="p">(</span><span class="n">a</span> <span class="o">==</span> <span class="mi">3</span><span class="p">,</span> <span class="n">b</span><span class="p">)</span>
<span class="go">masked_array(data=[--, 1, --, --],</span>
<span class="go">             mask=[ True, False,  True,  True],</span>
<span class="go">       fill_value=999999)</span>
</pre></div>
</div>
</dd></dl>

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